This invention relates to a vacuum coating apparatus having a vacuum chamber, having at least one cathode system, and having a system for the continuous transport of the substrates during the coating process, including endless transport means disposed pair-wise, which are guided in the manner of two parallel chain drives over sets of two wheels set apart from one another, thereby forming two straight runs, and to which the substrates can be fastened, thus enabling the substrates to be moved parallel to the cathode system.
In vacuum coating apparatus which are designed for a high throughput, the main problem lies in a precise and trouble-free transport of the largest possible number of substrates per unit of time through the actual coating zone or, in some cases, through a plurality of coating zones, and in some cases through still other pretreatment and after-treatment zones. It can be assumed that such treatment zones contained within a relatively larger vacuum chamber are separated from one another either by their principle of operation, and/or by special shielding, partition walls, etc. Examples of treatment stations are cathode sputtering systems, cathodic etching systems or glow discharge systems, preheating and afterheating stations, etc. In large industrial installations, the continuous or intermittent transport of substrates calls for appropriate mechanical construction measures, which inevitably produce at least some detritus, and inevitably, too, some of the coating material condenses upon the internal parts of the apparatus, and after a time it begins to flake off, resulting in the danger of contamination of the substrates.
When vacuum chambers are divided for the purpose of different process steps, it is customary to separate the compartments by means of flap valves. This necessitates separate transport systems for each chamber and complex electrical control and synchronization.
It is also possible to pass the substrates including their transport means through a number of chambers, in which case the partition walls contain slots for the passage of the substrates, and these slots are filled up as completely as possible by the substrate frames so as to prevent contamination. The passage of the substrate through the partition walls, however, requires high precision in the transport means. In addition, for the purpose of attaining short pump-down time, the volume of the chamber must be reduced to a minimum. These requirements are in some ways diametrically opposed, at least in large industrial plants, so that continuously or intermittent operating vacuum coating installations have hitherto not been widely used in practice.
German DDS No. 2,415,119 has disclosed a coating system of the general class described above, which consists substantially of a single, hollow-cylindrical cathode system, i.e., anode and cathode are constructed as portions of the periphery of a hollow cylinder surrounding the sputtering zone and provided with a plurality of longitudinal slits. The substrates are transported by means of a horizontal chain conveyor through a segment at the bottom of the horizontal, hollow-cylindrical cathode system, preferably in the horizontal position so that they can be coated on one side only. This means, of course, that the substrates can also run vertically to reduce the danger of contamination, but in this case evidently all that is thought of is substrates in a vertical position on the horizontal transport system. For stacking chambers containing substrate magazines or vacuum locks are to be situated at both ends of the sputtering chamber. However, the danger of contamination cannot be reduced in the described manner to the desirable degree. Contamination apparently was not very important in this known apparatus, since the embodiment presented is a laboratory system whose vacuum chamber is composed to an important degree of a glass receptacle. In the application of this principle of construction to a large industrial installation, the amount of space required in the horizontal direction is great, the cathodes are poorly accessible, and the sealing of the gaps in the individual partitions of the vacuum chamber is very unsatisfactory unless the transport system is horizontally guided with great precision.
But even in the evaporation type depositing systems frequently cited for purposes of comparison, the horizontal direction of transport has been used whenever flexible continuous conveyor means are used:
Thus it is known from German Pat. No. 1,183,337 to suspend plate-like substrates from a horizontal or slightly inclined frame and to carry them in the vertical position successively through a vacuum evaporation zone by means of a horizontal transport chain. As a result, very irregular coating density distributions are produced, since the vapor particles strike the substrate surface at different angles in each position of the substrates and with respect to each unit of the surface of the substrate.
German Pat. No. 1,236,900 has furthermore disclosed a vacuum evaporation apparatus having a conveyor chain circulating substantially in the horizontal direction. In the area of the bottom run of the chain, a plurality of plate-like substrates are arrayed in close order in a vertical position and picked up by the transport chain at certain intervals. The upper run of the chain passes over a plurality of evaporating crucibles. In order to obtain a uniform distribution of the coating thickness, the substrates, while being carried by the upper run of the chain, must be turned to a horizontal position by a special guiding means. Only in this manner it is possible to vapor coat the substrates on one side only. The simultaneous vapor coating of the upper surface, for example by means of special vapor guiding means, has proven impractical despite numerous attempts. With regard to space requirement and the difficulties involved if the vacuum chamber is divided into smaller chambers, the same disadvantages are encountered as in the method previously described.
It is also known to fasten substrates to cylindrical drums whose axis is horizontal. Vapor deposition in this case, however, takes place only on a small portion of the circumference of the drum, because the rest of it serves only as a magazine, and the height and breadth of a drum have an unfavorable influence on the dimensions and volume of the vacuum chamber. Such an apparatus is the subject matter of German Pat. No. 841,626.
Lastly, German DAS No. 2,420,430 also discloses the construction of cylindrical drums as holders of blade-shaped substrates. The drum, however, serves only as a magazine for the blades which are aligned radially with the drum axis, and for their transport. For the purpose of coating by vacuum deposition, the blades are individually shifted from the drum into coating chambers while they are in a substantially horizontal position. The vapor deposition apparatus involved is extraordinarily complex in construction and in operation; in addition, it requires a considerable amount of space due to the large drum diameter.